This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. As the realm of NMR-based metabolomics expands, more sensitive techniques need to be developed in order to attain more information per sample. One way to gain more information is to isotopically enrich samples with 13C. However, in most cases it is impractical or impossible to quantify this kind of data absolutely because doing so requires calibrating to 13C labeled metabolites. We are seeking to develop a method that will allow us to calibrate 13C enriched H-13C HSQC with standards that contain natural abundance carbon.